Roll stands of this type can have especially several backing rolls above and below the roll gap, for instance, one work roll that comes in direct contact with the rolling stock and in turn rolls on a usually larger backing roll or an intermediate roll, which in turn abuts another backing roll. The work rolls and/or the backing rolls and/or the intermediate rolls can be displaceable axially relative to each other. This way as a result of the shape of the surface of at least two rolls, targeted effects are possible with respect to the shape of the rolling stock running through the roll gap. The height of the roll gap is thereby intended to be adjustable, which requires a vertical displacement at the frame.
It is particularly difficult when in addition to the axial shifter, a work-roll bender is provided, even for a large roll intake, i.e. at large height of the roll gap, to guarantee the ability to set it. This is because in the bender, which is intended to counter-act a bending apart of the rolls that define the gap for the rolling stock, integrated locking elements as well as the guide elements for the axial shifter and the bearings for the rolls in the lateral beams of the frame, must be displaced and selected.
A roll stand is known from EP 1 436 104 [U.S. Pat. No. 7,310,985] with at least one axial shifter that makes it possible to set a large roll gap for rolling of thick blocks or slabs. In the known solution, the axial shifter is integrated into the construction components that retain the bearings for a work roll, so that a separate vertical displaceability of the axial shifter is no longer required.
The axial displacement of the work rolls is done by a shifter mounted coaxially on an insert of the work roll that is backed out of the frame with the set of rolls during a change of the work roll. In so-called “flying” work-roll bending, the upper work-roll inserts are supported by bending or balancing cylinders in U-shaped recesses of the upper backing-roll inserts. The bending cylinders can be located in the work-roll inserts or alternatively in the backing-roll inserts.
With a “flying” arrangement of the upper work roll, a very tall roll gap is conceivable. This would also make the rolling of thick blocks possible on such a roll stand. The work roll displacement and benders are backed out of the roll frame during a change of the set of rolls and can be maintained outside the roll frame. As a result, the operator does not have down time of the system while maintaining these units.
During axial displacement of the work roll, the upper work-roll assembly is pushed via the bending cylinders that serve to balance pressure into the upper backing-roll inserts. The frictional forces thus created generate moments of tilt that can bring about a skewing of the backing-roll inserts. In a sudden loading of the stand with roll force, the so-called tapping push, subsequent to the displacement of the work roll it can therefore not be precluded that at the backing roll bearing—in the case of flooded oil bearings—there is a high load between the bearing bushing and the stub or in the event of ball bearings, individual bearing rows experience high strain.
With the known work roll shifters and benders that avoid the disadvantage mentioned above, however, a roll rise, i.e. a roll gap for the throughput of rolling stock, can be set of only up to approximately 550 mm.